Liquid power-absorbing loads



April 28, 1970 s, GRIFFIN ET AL 3,509,496

' LIQUID POWERABSORBING LOADS Filed July 8, 1968 STEAM CONDENSER W WKMML M1;

ATTORNEYS United States Patent Oflice 3,509,496 Patented Apr. 28, 1970US. Cl. 33322 5 Claims ABSTRACT OF THE DISCLOSURE A light powerabsorbing load consists of a low loss dielectric insulating insert in atank. The tank is larger than the insert so that liquid in the tank hasaccess to the surface of the insert. The insert thus serves to guideradio frequency power to the liquid in the tank.

This invention relates to liquid power-absorbing loads and whilstprimarily concerned with liquid power-absorbing loads for absorbingunwanted power it is also applicable to liquid power-absorbing loads formeasuring power by calorimetric effects.

As at present known, the usual liquid power-absorbing load consists of alength of waveguide, normally some two or three feet long, with a glasstube running down the middle of it, power-absorbing liquid (usuallywater) being pumped through the tube via input and output waterconnections at its end. Not only is the glass tube itself, mounted inthis position, necessarily fragile but the water connections which passthrough the waveguide to its exterior are also liable to be broken.Another defect is that there is a tendency for steam to be evolved inthe conduit and if this happens it may seriously impair thepowerabsorbing capabilities of the load.

The present invention seeks to provide improved liquid power-absorbingloads in which the foregoing disadvantages are overcome or reduced.

According to this invention a liquid power-absorbing load comprises alow loss dielectric insulating insert in a tank the volume of which islarge relative to the volume of said insert and the liquid in which hasfree access to the surface of the insert inside the tank, said insertserving to guide radio frequency power to the liquid in the tank.

The insert is within a length of perforated waveguide which is insidethe tank, the perforations providing the liquid in the tank with freeaccess to the surface of the insert in said tank.

Preferably again said body is of tapered form to provide a suitableshape for boundary of the liquid to which the power to be absorbed isapplied.

Preferably again the body extends into the tank from Within a chokewaveguide section which is sealed into one wall of the liquid container.

Where the power to be absorbed is propagated in a rectangular waveguidea transformer wave guide section is preferably interposed between thechoke waveguide section and the rectangular waveguide in order toachieve good matching.

The liquid container may be open to the atmosphere but in practice thecontainer pefeably is sealed and a vapour condenser is provided tocondense any vapour evolved as a result of a rise in temperature of theliquid and return the vapour as liquid to said container.

The load may be employed simply to abesorb unwanted power or it may beused as a calorimetric power measuring device.

The invention is illustrated in and further described with reference tothe accompanying drawing which is a sectional view of a waterpower-absorbing load in accordance with the present invention.

Referring to the drawingthe load consists of a Cheby cheff waveguidetransformer section 1 which is stepped in its E dimension only. Theinput end 2 of the transformer section 1 is provided with a rectangularflange to which a rectangular waveguide (not shown) transmittingradiofrequency power to be absorbed in the load may be attached. Thewaveguide transformer section 1 feeds into a dielectric filled chokesection 3 which is sealed into the wall of a water-filled tank 4.Extending into the tank 4 form within the choke section 3 is a generallyrectangular sectioned tapered insert 5 of P.T.F.E. or other low lossdielectric insulating material which reduces in cross-section, as shown,along its length from the choke section 3 to maintain a suitable shapefor the boundary of the water to which the RF. power to be absorbed isapplied. The insert 5 is surrounded by a length of rectangular waveguide6 all four walls of which are perforated to provide the water in thetank with free access to the surface of the insert 5. Sealing againstwater from the tank 4 entering the transformer section 1 along thetapered insert 5 is provided by O-rings shown at 7.

The tank 4 may be open to the air so that any steam evolved may freelyescape or it may be sealed and a steam condenser 8 provided to condenseany steam and return it to the tank as water.

Although the example described above is for absorbing power propagatedin a waveguide, as will be understood, with suitable modification it mayequally be used to absorb power propagated along a co-axial conductor.

We claim:

1. A power absorbing load arrangement comprising a container, a liquidwithin said container, a low loss dielectric insert in said container,and a length of perforated waveguide inside said container andsurrounding said insert, the volume of asid container being largerelative to the volume of said insert, and said liquid having freeaccess to the surface of the insert inside the container through saidlength of perforated waveguide, whereby the insert serves to guide radiofrequency power to the liquid in the container.

2. A power absorbing load arrangement as claimed in claim 1 and whereinsaid insert is of tapered form to provide a suitable shape for boundaryof the liquid to which power to be absorbed is applied.

3. A power absorbing load arrangement as claimed in claim 1 and whereinthe insert extends into the container from within a choke waveguidesection which is sealed into one wall of the container.

A power absorbing load arrangement as claimed in claim 3, and whereinpower to be absorbed is propagated in a rectangular waveguide, andincluding a transformer guide section and the' rectangular-waveguide in-orde-r-------- to achieve good matching.

5. A power absorbing load arrangement as claimed in claim 1 and whereinthe container is sealed and a vapour 5 condenser is provlded to condenseany vapour evolved as a result of a rise in temperature of the liquidand return the vapour as liquid to said container.

References Cited 10 UNITED STAIES PATENTS 2,958,830 11/1960 Bird et al.-333-22 2,432,094 12/1947 Fox 1 33335 3,360,750 12/1967 Johnson 333-2215 FOREIGN PATENTS 908,808 10/1962 Great Britain.

' OTHER REFERENCES "Hig'h""Pressii're" Microwave "Window' Laws'on &Smith; The Review of Scientific Instruments, vol. 30, No. 11, November1959, pp. 989-991.

Catalog Microwave ComponentsElectronic Specialty (30., Los Angeles,Calif., Patent Ofiice Scientific Library, Jan. 21, 1965, cover page,page code E717 and page code E718.

Principles and Applications of Waveguide Transmismission, Southworth VanNostrand, Princeton, N.J., 1961, QC 661568, pp. 201-203.

HERMAN K. SAALBACHY, Primary Examine M. NUSS'BAUM', Assistantr ExaminerI

